In a medical setting, oxygen can be delivered to a patient from a cryogenic vessel, high pressure gas storage vessel or other controlled pressure delivery sources, such as a hospital delivery system. Such an oxygen delivery system includes an adjustable flow regulator to select a flow rate of oxygen to the patient. Adjustable flow regulators typically include a circular orifice plate having a plurality of apertures of varying sizes through which the oxygen can flow.
In order to create an aperture that allows a certain flow rate, users of prior art techniques typically create an undersized aperture using a hand tool, measure the flow rate, and subsequently increase the aperture size and measure the flow rate until gas flows at the desired rate. Other prior art methods utilize needle valves, stamping or compression of a large aperture, fabrication and assembly of discrete components, blockage of a flow conduit by a ball or tapered pin, photoetching of a thin metal disk which is subsequently attached to a thicker plate, or other largely manual methods.
To obtain an accurate flow rate, a real-time flow measurement is therefore made of each aperture during fabrication. Because this is largely a manual process, accurate registration is difficult to achieve, sometimes yielding a secondary aperture proximate to the main aperture to produce the proper flow rate. If the flow rate of a particular aperture is greater than a desired flow rate, then the entire part is rejected.